process tool including plasma spray for carbon nanotube growth

ABSTRACT

This invention provides a high volume manufacturing compatible process tool and method for integrating deposition of carbon nanotubes into device fabrication. A linear process tool for growing carbon nanotubes comprises a linear conveyor for moving a substrate through the linear process tool and a micro-plasma process unit including a plurality of micro-plasma spray guns arranged in an array, the micro-plasma process unit being positioned above the linear conveyor and configured to deposit material on the surface of the substrate as the substrate passes under the micro-plasma process unit on the linear conveyor. The micro-plasma process unit may include a first array of micro-plasma spray guns for depositing a catalyst material and a second array of micro-plasma spray guns for depositing the carbon nanotubes. A method of depositing carbon nanotubes on a substrate comprises: supplying a first precursor for a catalyst material to a first array of micro-plasma spray guns; creating a first plasma using the first array of micro-plasma spray guns and the first precursor; moving the substrate through the first plasma; activating the catalyst material; supplying a second precursor for the carbon nanotubes to a second array of micro-plasma spray guns; creating a second plasma using the second array of micro-plasma spray guns and the second precursor; moving the substrate through the second plasma.

FIELD OF THE INVENTION

The present invention relates generally to manufacturing tools andmethods, and more particularly to in-line processing tools forintegrating carbon nanotubes into electrical devices and semiconductordevices.

BACKGROUND OF THE INVENTION

Carbon nanotubes (CNTs) have electrical and mechanical properties thatmake them attractive for integration into a wide range of electronicdevices, including semiconductor devices. However, there is a need forcost effective and high-volume manufacturing (HVM) compatiblefabrication technologies to enable broad market applicability of suchdevices.

Carbon nanotubes are nanometer-scale cylinders with walls formed ofgraphene—single atom thick sheets of graphite. Nanotubes may be eithersingle-walled (cylinder wall composed of a single sheet of graphene,referred to as SWNTs) or multi-walled (cylinder wall composed ofmultiple sheets of graphene, referred to as MWNTs). Nanotubes havediameters as small as one nanometer, for a SWNT, and length to diameterratios of the order of 10⁶. Carbon nanotubes can have either metallic orsemiconducting electrical properties which make them suitable forintegration into a variety of devices, such as solar cells, for example.

Carbon nanotubes can be grown using a variety of techniques includingarc discharge, laser ablation and chemical vapor deposition. Most of thedevelopment of deposition processes for carbon nanotubes to date hasbeen in research laboratories and there is a paucity of work on HVMcompatible CNT deposition. Therefore, there is a need for HVM compatibleCNT deposition equipment and methods.

Furthermore, due to the unique properties of CNTs, it is desirable tointegrate CNTs into devices such as solar cells and semiconductordevices. The process conditions of the prevalent CNT growth processes,which may involve high temperatures and exposure to plasma, are notreadily compatible with many substrates and devices. Consequently, thereis a need for integration compatible processes for CNT growth.

Therefore, there remains a need for process equipment and methods thatcan significantly reduce the cost of integrating carbon nanotubes intoelectronic devices by enabling simplified, more HVM-compatibledeposition equipment and methods.

SUMMARY OF THE INVENTION

This invention provides a high volume manufacturing compatible processtool and method for integrating deposition of carbon nanotubes intodevice fabrication. Carbon nanotubes have attractive electrical andmechanical properties that make integration of carbon nanotubes into awide variety of electrical and semiconductor devices desirable. Theconcepts and methods of this invention allow for integration of carbonnanotube deposition into devices such as solar cells, batteries,capacitors, electrochromic devices, etc.

According to aspects of the invention a linear process tool for growingcarbon nanotubes comprises a linear conveyor for moving a substratethrough the linear process tool and a micro-plasma process unitincluding a plurality of micro-plasma spray guns arranged in an array,the micro-plasma process unit being positioned above the linear conveyorand configured to deposit material on the surface of the substrate asthe substrate passes under the micro-plasma process unit on the linearconveyor. The micro-plasma process unit may include a first array ofmicro-plasma spray guns for depositing a catalyst material and a secondarray of micro-plasma spray guns for depositing the carbon nanotubes. Anadvantage for process integration of the micro-plasma spray guns is thatthe plasma is a low temperature plasma which allows for carbon nanotubedeposition on temperature sensitive substrates.

According to further aspects of the invention a method of depositingcarbon nanotubes on a substrate comprises: supplying a precursor for thecarbon nanotubes to an array of micro-plasma spray guns; creating aplasma using the array of micro-plasma spray guns and the precursor; andmoving the substrate through the plasma.

According to yet further aspects of the invention a method of depositingcarbon nanotubes on a substrate comprises: supplying a first precursorfor a catalyst material to a first array of micro-plasma spray guns;creating a first plasma using the first array of micro-plasma spray gunsand the first precursor; moving the substrate through the first plasma;activating the catalyst material; supplying a second precursor for thecarbon nanotubes to a second array of micro-plasma spray guns; creatinga second plasma using the second array of micro-plasma spray guns andthe second precursor; and moving the substrate through the secondplasma.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 shows a schematic side view of a linear deposition tool of theinvention;

FIG. 2 shows a schematic top view of a linear deposition tool of theinvention;

FIG. 3 shows a schematic side view of the linear deposition tool of FIG.2, showing two alternative process gas supply configurations;

FIG. 4 shows a configuration of micro-plasma guns in a single processunit of a linear deposition tool of the invention;

FIG. 5 shows a vertical cross-sectional representation of a solar celldevice fabricated using the linear deposition tool of the invention; and

FIG. 6 shows a vertical cross-sectional representation of a structurewith vertically oriented carbon nanotubes fabricated using the lineardeposition tool of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings, which are provided as illustrative examples of theinvention so as to enable those skilled in the art to practice theinvention. Notably, the figures and examples below are not meant tolimit the scope of the present invention to a single embodiment, butother embodiments are possible by way of interchange of some or all ofthe described or illustrated elements. Moreover, where certain elementsof the present invention can be partially or fully implemented usingknown components, only those portions of such known components that arenecessary for an understanding of the present invention will bedescribed, and detailed descriptions of other portions of such knowncomponents will be omitted so as not to obscure the invention. In thepresent specification, an embodiment showing a singular component shouldnot be considered limiting; rather, the invention is intended toencompass other embodiments including a plurality of the same component,and vice-versa, unless explicitly stated otherwise herein. Moreover,applicants do not intend for any term in the specification or claims tobe ascribed an uncommon or special meaning unless explicitly set forthas such. Further, the present invention encompasses present and futureknown equivalents to the known components referred to herein by way ofillustration.

In general, the present invention contemplates a linear process toolcomprising micro-plasma process units. The linear process tool of theinvention may be used for growing carbon nanotubes as part of integrateddevice structures. Although the examples provided herein all includecarbon nanotubes, there is no intention to limit the invention todevices and methods for carbon nanotube growth. For example, the linearprocess tool of the invention may be used for integrating siliconnanoparticles into solar cell devices.

FIG. 1 shows a schematic representation of a linear process tool 100 ofthe invention. A substrate 110 is carried on a linear conveyor 112 inthe direction indicated. The substrate 110 may be glass, ceramic,plastic, polymer, semiconductor or any other suitable material on whichdeposition can be carried out. The substrate 110 may be a large formatsubstrate, with an area of up to two square meters and more, or acollection of smaller substrates, with areas of several squarecentimeters and less, for example, held in a suitable frame, as is wellknown in the industry. The substrate 110 may be rigid, for example asheet of glass, or flexible, for example a polymer film. The substrate110 may be an insulator, a semiconductor or a metal. Furthermore, thesubstrate 110 may be a continuous flexible substrate, in which case thelinear conveyor 112 is replaced by a reel-to-reel system fortransporting the continuous substrate through the tool 100. In preferredembodiments the substrate is moved continuously through the processsystem during processing. The process system is designed for highthroughput, with an expected linear speed of several meters per hour.Clearly, an equivalent tool configuration is a tool in which thesubstrate is stationary and the process unit/units are continuouslymoved over the substrate during processing. Yet further, the coordinatedcontrol of processing units and movement of the substrate may be used toprovide a large-area patterning of structures grown on the substrate.

The linear process tool 100 comprises serial process units. In theparticular embodiment shown in FIG. 1, the following process units areshown: a pre-heat unit 120; a micro-plasma process unit 130, comprisingan array of micro-plasma spray guns 131; thermal anneal units 140; and ashower-head plasma unit 150. This particular arrangement of processunits has been chosen for purposes of illustration. Many otherarrangements of process units are envisaged. For example, FIGS. 2 and 3show alternate micro-plasma process units 130 and annealing units 140.

The preheat unit 120 and the anneal units 140 may comprise halogenlamps, tungsten filaments, lasers, or other suitable sources of heat.The choice of heat source will be dependent on the substrate material,materials deposited and whether it is necessary to heat just the surfaceof the device being formed on the substrate, or to heat the entiresubstrate. Alternatively, the preheat and anneal units may be configuredto heat the substrate from below (not shown).

The micro-plasma process unit 130 comprises an array of micro-plasmaspray guns 131 which are fed from a common gas manifold 132 with eitherprocess gas or liquid. In the example shown in FIG. 1, process gas issupplied from a bubbler 134. Although, a liquid delivery system (notshown) may also be used to supply precursor to the micro-plasma guns131. Each micro-plasma gun 131 may consume approximately 5 to 50 Watts;each micro-plasma process unit, comprising typically 100 micro-plasmaspray guns 131, consumes approximately 500 to 5,000 Watts. Note that dueto micro-plasmas being low temperature plasmas, this may enabledeposition upon substrates comprising paper, plastics or polymers. Thedetails of micro-plasma spray guns are well known to those skilled inthe art of plasma deposition. Some examples of micro-plasma spray gunsare provided in U.S. Pat. No. 7,115,832 to Blankenship et al. and U.S.Patent Application Publication No. 2005/0008550 to Duan.

The shower-head plasma unit 150 may be configured to generate a plasma.The shower head 150 is preferably fabricated from ceramic material, towithstand the reactive free radicals that are generated in the plasma.The plasma can be generated by parallel plates, or an alternativeantennae, within the shower head 150. Alternatively, a plasma generatorcan be incorporated into the gas manifold 152. The shower head plasmaunit 150 is fed from a gas manifold 152 with a process gas. In theexample shown in FIG. 1, process gas is generated by pushing liquid fromsupply tank 154 through a liquid flow meter 156 and then through aninjector valve 158, which vaporizes the liquid into the manifold 152. Apush gas, such as nitrogen, helium, or other inert gas is used to pushthe liquid from the supply tank 154, as indicated by the arrows 155. Acarry gas, such as nitrogen may be used in the manifold 152—it flowsinto the manifold 152 as shown by the arrow 151. Generally the lines ofthe manifold 152 must be heated in order to avoid condensation ofprocess gas. Consequently, it is preferred that the length of the heatedmanifold lines is kept as short as can be accommodated. A second gasmanifold 153 can be used to supply further process gases. The showerhead plasma unit 150 may be used for plasma-enhanced chemical vapordeposition (PECVD) processes.

FIG. 2 is a schematic top view of a second embodiment of the linearprocess tool of the invention. A substrate 110 is carried on a linearconveyor 112 in the direction indicated under a plurality of processunits. In the linear process tool 200 the following alternating processunits are shown: micro-plasma process units 130, and thermal annealunits 140. This particular arrangement of process units is suitable forgrowing carbon nanotubes, as described with reference to FIG. 5 below.However, other process units may be used. For example, instead ofmicro-plasma process units 130, shower-head plasma units 150 may be usedinstead. The order and choice of process units is completely variable tofit the process requirements.

FIG. 3 shows a schematic side view of the linear process tool 200. Asubstrate 110 is carried on a linear conveyor 112 in the directionindicated under a plurality of alternating process units 130 and 140.Gas sources 336 and 338 provide process gases to the process units 130,through gas manifolds 331 and 333 respectively. The two gas supplysystems are shown as alternatives in FIG. 3; although, both may be usedin parallel to supply different process gases. An importantconsideration for the linear process tool of the invention is reducingthe cost of the tool by efficient design of aspects such as process gassupply. The two alternatives shown in FIG. 3 illustrate the use of onegas supply system for either two or four process units. The limit in alinear process tool as to how many process units can be supplied from asingle manifold and source is generally going to be the path lengthbetween the process gas source and the process unit. This isparticularly the case for process gases which readily condense on theinterior surfaces of the manifold. (Heated manifolds may be used toovercome this problem; however, heated manifolds are expensive tofabricate and operate).

FIG. 4 is a top view of the micro-plasma process unit 130 showing anexample of a configuration of micro-plasma spray guns 131. Themicro-plasma process unit 130 may contain approximately 100 micro-plasmaspray guns 131 in order to achieve the desired uniformity of deposition.However, for ease of illustration only 28 micro-plasma spray guns 131are shown in FIG. 4. The guns 131 are arranged to provide uniformdeposition on a substrate, as the substrate is carried under the processunit. See FIGS. 1-3. Other configurations may be used to achieve uniformdeposition, dependent on the specific properties of the micro-plasmaguns. Furthermore, the micro-plasma process unit 130 may be separatedinto two, or more, banks of plasma guns 131; for example, the guns 131to the right of dashed line 132 may be used for catalyst deposition andthe guns 131 to the left of the dashed line 132 may be used for carbonnanotube deposition, where the substrate 110 is moving under the processunit 130 from right to left. In this case, where several banks of gunsexist within a single micro-plasma process unit, each bank of guns willhave its own precursor supply and operating control system.

FIG. 6 shows a cross-sectional representation of a substrate 110 withcatalyst particles 602 and nanotubes 604. The catalyst particles andnanotubes can be deposited using the linear process tool of theinvention. Methods for deposition of the carbon nanotubes are asfollows, with reference to FIG. 1.

A first method for growing carbon nanotubes comprises the followingsteps. Providing a substrate 110 with catalyst material 602 on thesurface. The catalyst material 602 may be a transition metal such as Co,Ni, and Fe, or a transition metal alloy such as Fe—Ni, Co—Ni and Mo—Ni.Heating the catalyst material 602 using a preheat unit 120 prior to thedeposition of nanotubes—generally the catalyst must be activated byheating in order to grow nanotubes. (There is also the option of heatingthe substrate from below in order to activate the catalyst). Growingcarbon nanotubes on the catalyst material using a micro-plasma unit 130.The micro-plasma unit 130 is supplied with precursor compounds such asxylene and ethanol. Mixtures of precursor compounds may also be used.

A second method for growing carbon nanotubes comprises the followingsteps. Providing a substrate 110 with catalyst material 602 on thesurface. Heating the catalyst material 602 while growing carbonnanotubes on the catalyst material using a micro-plasma unit 130.

A third method for growing carbon nanotubes comprises the followingsteps. Providing a substrate 110 with catalyst material 602 on thesurface. Growing carbon nanotubes on the catalyst material using amicro-plasma process unit 130, where the micro-plasma activates thecatalyst allowing the growth of nanotubes. In some cases, activation ofthe catalyst material by the micro-plasma unit may be at roomtemperature. Furthermore, the micro-plasma may be effective inchemically reducing the catalyst material and providing a desirablesurface of carbon nanotube growth.

A fourth method for growing carbon nanotubes comprises the followingsteps. Growing catalyst material 602 on the surface of substrate 110using a first micro-plasma unit 130. A suitable precursor materialdelivered to the micro-plasma spray guns 131 is ferocene, for depositionof an iron catalyst. Activating the catalyst material using a pre-heatunit 120. Growing carbon nanotubes on the catalyst material using amicro-plasma process unit 130, where the micro-plasma activates thecatalyst allowing the growth of nanotubes.

A fifth method for growing carbon nanotubes comprises the followingsteps. Depositing catalyst material while growing carbon nanotubes,using a micro-plasma process unit 130 configured, as described above, todeposit both catalyst and carbon nanotube precursor materials fromseparate banks of micro-plasma spray guns 131 within a singlemicro-plasma process unit 130. The substrate is moved under the separatebanks so as to be coated in catalyst material prior to carbon nanotubegrowth. As above, a pre-heating step may be used, heating during growthmay be used, or in some cases heating may not be needed—the micro-plasmaitself may be effective in activating the catalyst.

A sixth method for growing carbon nanotubes comprises the followingsteps. Depositing catalyst material and growing carbon nanotubessimultaneously using a micro-plasma process unit 130 supplied with amixture of precursors for both catalyst material and carbon nanotubes.Again, a pre-heating step may be used, heating during growth may beused, or in some cases heating may not be needed—the micro-plasma itselfmay be effective in activating the catalyst.

The carbon nanotubes may be grown with a vertical orientation, as shownin FIG. 6, by controlling the micro-plasma deposition conditions.Biasing the substrate relative to the micro-plasma process unit 130during carbon nanotube growth may enhance the vertical orientation ofthe carbon nanotubes.

FIG. 5 shows a cross-sectional representation of a solar cell device 500which may be manufactured using the process tool of the invention. Thedevice 500 is comprised of a plurality of layers formed on a p-typedoped silicon substrate 502. The substrate 502 may be a silicon wafer,or a polycrystalline substrate. There is a layer of p⁺-type dopedsilicon 501 on the bottom surface of the substrate 502. On the topsurface of the substrate are: an n-type doped layer 503; a p-type dopedlayer 504; a stack of layers 505-508 which are comprised of siliconnanocrystals 520 and carbon nanotubes 530 in a matrix of Si0₂, SiC_(x),SiN_(x) and similar insulators; and a layer of n-type doped silicon 509.The silicon nanocrystals 520 may be polydisperse or monodisperse and mayhave random or specific orientations. Preferably the siliconnanocrystals are quantum dots. (A quantum dot is a semiconductor ofsufficiently small dimensions to confine excitons in three dimensions,where an exciton is a bound electron-hole pair in the semiconductor).Furthermore, in place of silicon nanoparticles, copper indium galliumselenide (CIGS) nanoparticles may be deposited.

Layers 505-508 of solar cell device 500 may be fabricated using thelinear process tool of the invention as described herein. A method forgrowing a layer 505 of the device 500 comprises the following steps.Preheating the substrate using a pre-heat unit 120. Depositing a siliconrich insulating film using a PECVD shower-head plasma unit 150 or amicro-plasma process unit 130. The film is in the range of 2 to 15nanometers thick. (For example, the CVD process may utilize acombination of the following process gases: SiH4, Si2H6, NH3 and H2.This results in a silicon-rich silicon nitride film.) Annealing thesilicon-rich silicon nitride film using an annealing unit 140. Theannealing process is tailored to grow silicon nanocrystals within thenitride thin film, where the diameter of the nanocrystals is preferablyless than 5 nanometers and the nanocrystals are quantum dots. Growingcatalyst material on the surface of the annealed film using amicro-plasma unit 130, followed by growing carbon nanotubes 530 on thecatalyst material using either the same or a different micro-plasma unit130. Note that the carbon nanotubes 530 may form a continuous layer, ordiscontinuous layer, depending on the coverage of the catalyst material.The carbon nanotubes 530, in FIG. 5, are shown connecting the siliconnanocrystals 520. This representation is used in order to emphasize therole of the carbon nanotubes 530 in enabling charge transfer to and fromthe silicon nanocrystals 520, and is not meant to indicate that thecarbon nanotubes 530 are limited to being grown only where siliconnanocrystals 520 exist. The process described above is repeated for eachlayer of the stack 505-508.

Further to the solar cell shown in FIG. 5, other solar cellconfigurations may be manufactured using the linear process tool of theinvention. For example, silicon nanocrystals may be deposited on atransparent conductive oxide (TCO) or other substrate. CIGSnanoparticles may be deposited.

The linear process tool of the invention and the methods described abovemay be used to grow nanoparticles and nanotubes as an integrateddeposition process in the formation of solar cells, Li ion batteries,supercapacitors, displays, electrochromic devices, etc. Variousprocesses may readily be integrated into the linear process tool of theinvention, such as plasma-enhanced chemical vapor deposition (PECVD).

The methods described above for growing nanotubes and nanoparticles mayalso be implemented on process equipment such as the Applied Materials'Producer™ platform which has a platform architecture with Twin Chamber™modules to achieve high throughput. The Twin Chamber™ unit can beconfigured for growth of carbon nanotubes, and up to three Twin Chamber™units can be accommodated on one Producer™ platform.

Although the present invention has been particularly described withreference to the preferred embodiments thereof, it should be readilyapparent to those of ordinary skill in the art that changes andmodifications in the form and details may be made without departing fromthe spirit and scope of the invention. It is intended that the appendedclaims encompass such changes and modifications.

1. A linear process tool for growing carbon nanotubes comprising: alinear conveyor for moving a substrate through said linear process tool;a micro-plasma process unit including a plurality of micro-plasma sprayguns arranged in an array, said process unit being positioned above saidlinear conveyor and configured to deposit material on the surface ofsaid substrate as said substrate passes under said micro-plasma processunit on said linear conveyor; and a heating unit configured to heat thesurface of said substrate as said substrate passes under said heatingunit on said linear conveyor.
 2. A linear process tool as in claim 1wherein said substrate is a large area substrate.
 3. A linear processtool as in claim 2 wherein said substrate has an area greater than onesquare meter.
 4. A linear process tool as in claim 1 wherein saidsubstrate is a sheet of flexible material and said linear conveyor movessaid sheet from a first reel at a first end of said linear process toolto a second reel at a second end of said linear process tool.
 5. Alinear process tool as in claim 1 wherein said micro-plasma process unitincludes: a first array of micro-plasma spray guns for depositing acatalyst material; and a second array of micro-plasma spray guns fordepositing said carbon nanotubes; wherein said first array and saidsecond array are configured so that said substrate moves on said linearconveyor under said first array and then under said second array.
 6. Alinear process tool as in claim 1 wherein said substrate is electricallybiased with respect to said micro-plasma process unit.
 7. A linearprocess tool as in claim 1 further comprising a shower-head plasmadeposition unit, said shower-head plasma deposition unit beingpositioned above said linear conveyor and configured to deposit materialon the surface of said substrate as said substrate passes under saidshower-head plasma deposition unit on said linear conveyor.
 8. A linearprocess tool as in claim 7 wherein said shower-head plasma depositionunit is made of ceramic material.
 9. A method of depositing carbonnanotubes on a substrate comprising: supplying a precursor for saidcarbon nanotubes to an array of micro-plasma spray guns; creating aplasma using said array of micro-plasma spray guns and said precursor;and moving said substrate through said plasma.
 10. A method ofdepositing carbon nanotubes as in claim 9 wherein said precursorincludes a mixture of xylene and ferocene.
 11. A method of depositingcarbon nanotubes as in claim 9 further comprising applying an electricalbias between said substrate and said array of micro-plasma spray guns.12. A method of depositing carbon nanotubes as in claim 9 furthercomprising, before said creating step, applying a catalyst material tosaid substrate.
 13. A method of depositing carbon nanotubes as in claim12 further comprising activating said catalyst material.
 14. A method ofdepositing carbon nanotubes as in claim 13 wherein said activatingincludes heating said catalyst material.
 15. A method of depositingcarbon nanotubes on a substrate comprising: supplying a first precursorfor a catalyst material to a first array of micro-plasma spray guns;creating a first plasma using said first array of micro-plasma sprayguns and said first precursor; moving said substrate through said firstplasma; activating said catalyst material; supplying a second precursorfor said carbon nanotubes to a second array of micro-plasma spray guns;creating a second plasma using said second array of micro-plasma sprayguns and said second precursor; and moving said substrate through saidsecond plasma.
 16. A method of depositing carbon nanotubes on asubstrate as in claim 15 wherein said activating includes heating saidcatalyst material.
 17. A method of depositing carbon nanotubes on asubstrate as in claim 15 wherein said activating includes exposing saidcatalyst material to said second plasma.
 18. A method of depositingcarbon nanotubes on a substrate as in claim 15 wherein said first arrayof micro-plasma spray guns and said second array of micro-plasma sprayguns are in the same micro-plasma deposition unit.